In order to fight death worms, get a rex with around 10k health and 200% melee damage. This lets you tank it while dealing loads of damage.

for the love of god don’t try to kill it with a mana. it takes reduced damage or something, took me an hour to get it to half health with my mana

On Ragnarok I had the 'best' surprise ever and encountered one not knowing what the heck was happening I was gathering meat from killing animals and noticed some dust following me I stayed to see what it was and a giant worm appeared and killed my pteranodon and me along with it

Interestingly if you come into an assumed view range of a Deathworm a bug, Pune not intended, allows the Deathworm to be seen for a brief second, allowing one to prepare against either attack or attacking the monster.